How compounding builds the balance
Each compounding period the account earns interest on whatever is sitting in it — including interest credited in earlier periods. That feedback loop is what separates compound interest from simple interest, where only the original deposit ever earns.
Compounding more often nudges the result upward because interest starts earning interest sooner. Going from annual to monthly compounding at the same stated rate gives a slightly higher ending balance, though the gap is smaller than most people expect.
Reading the growth curve
The line chart traces the balance year by year. It starts out looking almost straight, then bends upward as the years pass — that upward curve is compounding at work. The longer the horizon, the more dramatic the bend becomes.
The donut splits the final balance into the money you put in versus the interest the account generated. Over long periods the interest slice can grow larger than the principal slice, which is the whole appeal of leaving money invested.
Tips for getting the most from it
A few habits make compounding work harder for you:
- Start early — time in the market matters more than the exact rate.
- Avoid withdrawing earnings, since every dollar taken out stops compounding.
- Compare accounts by their effective annual yield, not just the headline rate, to capture the compounding frequency.
What this estimate assumes
This model uses a single lump-sum deposit, a fixed rate, and no further contributions, taxes, or fees. Real returns fluctuate, and taxes on interest can reduce what you keep. Treat the figure as a clean illustration of the math rather than a guaranteed outcome.
Formula
amount = P·(1 + (rate/100)/m)^(m·years)